10/10 should be reserved for a once in a console generation game that revolutionizes a genre. While any artistic effort has some flows, a 10/10 game should do nothing poorly and complaints should be limited to minor details and individual preferences that don't impact game play. Hardware limitations should be taken into account of course, but then again a great designer works around those limitations, not against them. Anything less than all that deserves a 9.x at best, IMO.
The controls of MGS4 alone should limit that game from getting anything higher than a 9.5-9.9. Japanese designers just don't seem to "get" the 1st/3rd person shooter. And GTA4 was great, but it was basically GT3 with prettier graphics and a totally overrated story. Evolution, not revolution and in my book that means a 9.9.
Seriously, the people who rave about how "fucking awesome and Oscar worthy and Godfather-like" GTA4's story was need to actually WATCH the Godfather again, and maybe read a fucking book. It's good for a video game, but that's not saying much.
I like HL2 and the sequels, and they're very well made, but I wish they were a bit harder and I wish the enemy AI was a bit better. Even on the hardest difficulty it's usually pretty easy to sit back and let the enemies come to you and make stupid mistakes. Headshot-headshot-headshot. And there are so many tight corridors and so many enemies that seem to come from one place that it's easy to just line them up and mow them down without having to deal with many at a time. A single exploding barrel fired from the gravity gun often takes out 4-5 enemies, the only 4-5 enemies you'll have to face for the next three minutes. They may very well have one of the best stories and some of the best, least-grating dialogue and voice acting as well, but the action sometimes leaves a bit to be desired. More open environments and more viscious enemies would be a welcome addition to HL2:3.
That said I bought the Orange Box and HL2:ep3 is definitely on my "to buy" list, I do consider it one of the finest FPSs out there.
I would have paid $30 just to have Portal, that game is the shit. It's only fault is that it's too short, but for what it is, it's close to a perfect game. A 9.9 or maybe even a 10/10 is honestly deserved in that case. I'm not sure the Orange Box would deserve a 10/10 if it wasn't for that game, unless one is talking about value/$$$.